The introduction of liquid fertilizer or other liquid additive into a sprinkler system pipeline from a reservoir has been known in the prior art. The present invention, however, utilizes a liquid fertilizer cartridge that dispenses a pre-determined volume of fertilizer into a mixing chamber with each water application where the fertilizer is mixed in the mixing chamber with water and the mixture then enters the water flow in the sprinkler system pipeline. In the prior art, a multiplicity of membranes have been used where each was responsive to water pressure differences across the membrane to open and close flow paths permitting fertilizer to flow directly into the sprinkler system pipeline where it mixed with the water flow to the sprinkler. The present invention has a single diaphragm that is responsive to spring forces and water pressure in the pipeline and the fertilizer is mixed in the mixing chamber before entering the pipeline which permits a more uniform distribution of the fertilizer into the waterflow.
In U.S. Pat. No. 3,367,353 a device is described for injecting liquid fertilizer into a sprinkler system. The device of the U.S. Pat. No. 3,367,353 utilizes two flexible diaphragms and a spool valve to achieve the desired injection function at the start of the cycle. The U.S. Pat. No. 3,367,353 is responsive to substantial pressure differences across the diaphragms to operate and requires a differential pressure to inject the fertilizer into the water stream. The discharge line of the U.S. Pat. No. 3,367,353 through which the fertilizer enters the water stream remains filled with fertilizer after an irrigation cycle and the fertilizer has continuous access to the downstream leg of the system when the irrigation cycle is completed.
It is desirable to provide a device that dispenses fertilizer over a period of time to evenly distribute the fertilizer rather than to dispense the fertilizer as an immediate slug. It is further desirable to provide a device that does not require differential pressures to inject the fertilizer and which reduces the pressure loss and impedance of water flow resulting from the creation of the differential pressures within the pipeline. Another desirable feature in the present invention is that substantially all of the fertilizer charged in the fertilizer chamber is mixed in the mixing chamber when the injection cycle of the fertilizer into the system is completed.